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Publication numberUS4588553 A
Publication typeGrant
Application numberUS 06/468,592
Publication dateMay 13, 1986
Filing dateFeb 22, 1983
Priority dateFeb 26, 1982
Fee statusPaid
Also published asCA1228252A1, DE3366165D1, EP0088511A1, EP0088511B1
Publication number06468592, 468592, US 4588553 A, US 4588553A, US-A-4588553, US4588553 A, US4588553A
InventorsBrian Evans, Christopher J. Peel
Original AssigneeThe Secretary Of State For Defence In Her Brittanic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
For use in aeospace airframe structures
US 4588553 A
Abstract
Aluminium alloys having compositions within the ranges (in wt %) 2 to 2.8 lithium--0.4 to 1 magnesium--1 to 1.5 copper--0 to 0.2 zirconium--0 to 0.5 manganese--0 to 0.5 nickel--0 to 0.5 chromium--balance aluminium. The alloys are precipitation hardenable and exhibit a range of properties, according to heat treatment, which make them suitable for engineering applications where light weight and high strength are required.
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Claims(10)
We claim:
1. An aluminium based alloy consisting essentially of in weight percent;
______________________________________Lithium      2.0 to 2.8Magnesium    0.4 to 1.0Copper       1.0 to 1.5Zirconium      0 to 0.2Manganese      0 to 0.5Nickel         0 to 0.5Chromium       0 to 0.5Aluminium    Balance (except for        incidental impurities).______________________________________
2. An aluminium alloy according to claim 1, said alloy being produced by an ingot metallurgy route.
3. An aluminium alloy according to claim 1, said alloy having a magnesium content in the range 0.7 to 1.0 weight percent.
4. An aluminium alloy consisting essentially of in weight percent
______________________________________Lithium    2.32Magnesium  0.5Copper     1.22Zirconium  0.12Aluminium balance (except for incidental impurities).______________________________________
5. An aluminium alloy consisting essentially of in weight percent;
______________________________________Lithium    2.44Magnesium  0.56Copper     1.18Zirconium  0.13Aluminium balance (except for incidental impurities).______________________________________
6. An aluminium alloy consisting essentially of in weight percent;
______________________________________  Lithium         2.56  Magnesium       0.73  Copper          1.17  Zirconium       0.08  Aluminium balance (except for incidental  impurities)______________________________________
7. An aluminium alloy consisting essentially of in weight percent;
______________________________________  Lithium         2.21  Magnesium       0.67  Copper          1.12  Zirconium       0.10  Aluminium balance (except for incidental  impurities)______________________________________
8. An aluminium alloy consisting essentially of in weight percent;
______________________________________  Lithium         2.37  Magnesium       0.48  Copper          1.18  Zirconium       0.11  Aluminium balance (except for incidental  impurities)______________________________________
9. An aluminium alloy consisting essentially of in weight percent;
______________________________________  Lithium         2.48  Magnesium       0.54  Copper          1.09  Zirconium       0.12  Nickel          0.31  Aluminium balance (except for incidental  impurities)______________________________________
10. An aerospace airframe structure produced from an aluminium alloy according to claim 1.
Description

This invention relates to aluminium alloys containing lithium, in particular to those alloys suitable for aerospace applications.

It is known that the addition of lithium to aluminium alloys reduces their density and increases their elastic moduli producing significant improvements in specific stiffnesses. Furthermore the rapid increase in solid solubility of lithium in aluminium over the temperature range 0 to 500 C. results in an alloy system which is amenable to precipitation hardening to achieve strength levels comparable with some of the existing commercially produced aluminium alloys.

Up to the present time the demonstrable advantages of lithium containing alloys have been offset by difficulties inherent in the actual alloy compositions hitherto developed and the conventional methods used to produce those compositions. Only two lithium containing alloys have achieved significant usage in the aerospace field. These are an American alloy, X2020 having a composition Al--4.5Cu--1.1Li--0.5Mn--0.2Cd (all figures relating to composition now and hereinafter are in wt%) and a Russian alloy, 01420, described in U.K. Pat. No. 1,172,736 by Fridlyander et al and containing Al--4 to 7 Mg--1.5 to 2.6 Li--0.2 to 1.0 Mn--0.05 to 0.3 Zr (either or both of Mn and Zr being present.

The reduction in density associated with the 1.1% lithium addition to X2020 was 3% and although the alloy developed very high strengths it also possessed very low levels of fracture toughness making its efficient use at high stresses inadvisable. Further ductility relates problems were also discovered during forming operations.

The Russian alloy 01420 possesses specific moduli better than those of conventional alloys but its specific strength levels are only comparable with the commonly used 2000 series aluminum alloys so that weight savings can only be achieved in stiffness critical applications.

Both of the above alloys were developed during the 1950's and '60's a more recent alloy published in the technical press has the composition Al--2Mg--1.5Cu--3Li--0.18Zr. Whilst this alloy possesses high strength and stiffness the fracture toughness is still too low for many aerospace applications. In attempts to overcome problems associated with high solute contents such as, for example, cracking of the ingot during casting or subsequent rolling, many workers in the field have turned their attention to powder metallurgy techniques. These techniques whilst solving some of the problems of a casting route have themselves many inherent disadvantages and thus the problems of one technique have been exchanged for the problems of another. Problems of a powder route include those of removal of residual porosity, contamination of powder particles by oxides and practical limitations on size of material which can be produced.

It has now been found that relatively much lower additions of the alloying elements magnesium and copper may be made and by optimising the production process parameters and subsequent heat treatments alloys possessing adequate properties including a much higher fracture toughness may be produced.

In the present alloys, the alloy composition has been developed to produce an optimum balance between reduced density, increased stiffness and adequate strength, ductility and fracture toughness to maximise the possible weight savings that accrue from both the reduced density and the increased stiffness.

According to the present invention, therefore, an aluminium based alloy has a composition within the following ranges, the ranges being in weight percent:

______________________________________  Lithium 2.0 to 2.8  Magnesium          0.4 to 1.0  Copper  1.0 to 1.5  Zirconium            0 to 0.2  Manganese            0 to 0.5  Nickel    0 to 0.5  Chromium            0 to 0.5  Aluminium          Balance______________________________________

Optional additions of one or more of the elements zirconium, manganese, chromium and nickel may be made to control other metallurgical parameters such as grain size and grain growth on recrystallisation.

A preferred range for a zirconium addition would be 0.1 to 0.15 weight percent.

A major advantage of the more dilute lithium containing alloys is that production and processing are greatly facilitated. Alloys according to the present invention may be produced by conventional casting techniques such as, for example, direct chill semi-continuous casting. The casting problems associated with known alloys have led many workers to use production techniques based on powder metallurgy routes.

Owing to their lower solute contents the present alloys are more easily homogenised and subsequently worked than previous alloys having relatively high solute contents.

Because of their advantageous mechanical and physical properties including low density and excellent corrosion resistance, the latter property also being partly attributable to the lower solute content, the alloys are particularly suitable for aerospace airframe applications. The density of an alloy having the composition Al--2.44Li--0.56Mg--1.18Cu--0.13Zr is 2.54 g/ml this compares favourably with the density of 2014 alloy, the example, which is 2.8 g/ml. This is a density reduction of over 9% on a conventional alloy having comparable properties. It will be appreciated that alloys of the present invention also enjoy an additional advantage by virtue of their lower solute content in that they have less of the heavier elements which increase density.

In sheet applications a preferred magnesium content is approximately 0.7%. It has been found that the magnesium level is critical in terms of the precipitating phases and subsequent strength levels.

Examples of alloys according to the present invention will now be given together with properties and corresponding heat treatment data.

EXAMPLE No. 1 Composition Al--2.32Li--0.5Mg--1.22Cu--0.12Zr

The alloy ingot was homogenised, hot-worked to 3 mm thickness and cold rolled to 1.6 mm with inter stage annealing.

The alloy sheet was then solution treated, cold water quenched and stretched 3%.

Table 1 below gives average test results for the various ageing times at 170 C.

              TABLE 1______________________________________Ex-          0.2%                        Fractuream-  Ageing  Proof   Tensile      Elastic                                    Toughnessple  time    Stress  Strength                       Elong Modulus                                    Kc,No   (hrs)   MPa     MPa    %     E.GPa  MPa√m______________________________________1     11/2   326     414    6.5   76.7   87.91     5      381     450    4.5   80.0   68.31     8      389     458    4.5   79.5   79.71    24      426     489    3.5   80.2   64.81    64      455     503    6.0   83.0   46.5______________________________________
EXAMPLE No. 2 Composition Al--2.44Li--0.56Mg--1.18Cu--0.13Zr

Alloy processing details as for Example No. 1. Test results are given below in Table 2.

              TABLE 2______________________________________Ex-          0.2%                        Fractuream-  Ageing  Proof   Tensile      Elastic                                    Toughnessple  time    Stress  Strength                       Elong Modulus                                    Kc,No   (hrs)   MPa     MPa    %     E.GPa  MPa√m______________________________________2    11/2    313     389    7.2   78.8   79.22    8       391     464    6.2   78.0   --______________________________________
EXAMPLE No. 3 Composition Al--2.56Li--0.73Mg--1.17Cu--0.08Zr

Alloy processing details as for Example No. 1 except that the stretching was 2%. Test results are given below in Table 3.

              TABLE 3______________________________________  Ageing  0.2% Proof                    Tensile       ElasticExample  (time)  Stress    Strength                            Elong ModulusNo     (hrs)   MPa       MPa     %     E.GPa______________________________________3       8      409       489     6.6   79.83      24      416       477     5.5   --3      40      457       518     5.5   --______________________________________
EXAMPLE No. 4 Composition Al--2.21Li--0.67Mg--1.12Cu--0.10Zr

Alloy processing details as for Example No 3. Test results are given below in Table 4.

              TABLE 4______________________________________Ex-          0.2%                        Fractuream-  Ageing  Proof   Tensile      Elastic                                    Toughnessple  time    Stress  Strength                       Elong Modulus                                    Kc,No   (hrs)   MPa     MPa    %     E.GPa  MPa m______________________________________4     8      378     447    6.5   78.7   71.34    24      399     468    6.0   78.0   62.9______________________________________
EXAMPLE No. 5 Composition Al--2.37Li--0.48Mg--1.18Cu--0.11Zr

The alloy of this example was tested in the form of 11 mm thick plate.

Average figures are given of longitudinal and transverse test pieces in Table 5 below.

The alloy has not been cross-rolled.

              TABLE 5______________________________________  Ageing  0.2% Proof                    Tensile       ElasticExample  time    Stress    Strength                            Elong ModulusNo     (hrs)   MPa       MPa     %     E.GPa______________________________________5       8      340       431     7.8   82.95      16      389       458     7.1   82.45      24      399       469     7.0   82.05      48      422       490     6.9   80.65      72      432       497     6.5   81.6______________________________________
EXAMPLE No. 6 Composition Al--2.48Li--0.54Mg--1.09Cu--0.31Ni--0.12Zr

The alloy of this example was tested in the form of 25 mm hot-rolled plate solution treated at 530 C., water quenched and stretched 2%. Test results are given below in Table 6.

              TABLE 6______________________________________   Ageing   Ageing  0.2% Proof                            TensileExample Temp     Time    Stress  Strength                                   ElongNo      (C.)            (hrs)   MPa     MPa    %______________________________________6       170      16      324     405    6.56       "        48      389     444    4.86       "        72      393     462    4.86       190      16      358     433    7.16       "        48      433     482    5.5______________________________________

Although all of the material for the examples given above was produced by conventional water cooled chill casting processes the alloy system is however amenable to processing by powder metallurgy techniques. It is considered, however, that a major advantage of the alloys of the present invention lies in the ability to cast large ingots. From such ingots it is possible to supply the aerospace industry with sizes of sheet and plate comparable with those already produced in conventional aluminium alloy.

The examples given above have been limited to material produced in sheet and plate form. However, alloys of the present invention are also suitable for the production of material in the form of extrusions, forgings and castings.

Alloys of the present invention are not limited to aerospace applications. They may be used wherever light weight is necessary such as, for example, in some applications in land and sea vehicles.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2381219 *Oct 12, 1942Aug 7, 1945Aluminum Co Of AmericaAluminum alloy
US2915390 *Jan 13, 1958Dec 1, 1959Aluminum Co Of AmericaAluminum base alloy
US2915391 *Jan 13, 1958Dec 1, 1959Aluminum Co Of AmericaAluminum base alloy
CH216204A * Title not available
DE1927500A1 *May 30, 1969Feb 11, 1971Max Planck GesellschaftLithium containing aluminium alloys
DE2127909A1 *Jun 4, 1971Dec 28, 1972Max Planck GesellschaftAluminium alloys - contg lithium, magnesium and zinc
FR518023A * Title not available
FR1148719A * Title not available
FR1161306A * Title not available
FR2190930A1 * Title not available
GB1172736A * Title not available
GB1572587A * Title not available
Non-Patent Citations
Reference
1"Aluminium und Aluminiumlegierungen", by Dr. D. Altenpohl, p. 705, 1965.
2"Improved Aluminum Alloys for Airframe Applications", by M. W. Hyatt et al., Mar. 1977, pp. 56-59, Metal Progress.
3 *Aluminium und Aluminiumlegierungen , by Dr. D. Altenpohl, p. 705, 1965.
4 *American Metal Market/Metal Working News of 29 Dec. 1980.
5 *Improved Aluminum Alloys for Airframe Applications , by M. W. Hyatt et al., Mar. 1977, pp. 56 59, Metal Progress.
6 *Lockheed Report No. LMSC D766966 (Sept. 1980) p. 10.
7Lockheed Report No. LMSC-D766966 (Sept. 1980) p. 10.
8Proceedings "First International Aluminum-Lithium Conference", 19-21 May 1980, Pub. Metallurgical Society of AIME.
9 *Proceedings First International Aluminum Lithium Conference , 19 21 May 1980, Pub. Metallurgical Society of AIME.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4861551 *Jul 30, 1987Aug 29, 1989The United States Of America As Represented By The Administrator, National Aeronautics And Space AdministrationElevated temperature aluminum alloys
US4894096 *Jun 23, 1986Jan 16, 1990Cegedur PechineyHot working, copper, zinc, casting, quenching
US5032359 *Mar 23, 1989Jul 16, 1991Martin Marietta CorporationUltra high strength weldable aluminum-lithium alloys
US5085830 *Mar 24, 1989Feb 4, 1992Comalco Aluminum LimitedProcess for making aluminum-lithium alloys of high toughness
US5122339 *Feb 22, 1990Jun 16, 1992Martin Marietta CorporationAluminum-lithium welding alloys
US5133931 *Aug 28, 1990Jul 28, 1992Reynolds Metals CompanyLithium aluminum alloy system
US5160555 *Feb 27, 1991Nov 3, 1992The Boeing CompanyAluminum-lithium alloy article
US5198045 *May 14, 1991Mar 30, 1993Reynolds Metals CompanyLow density high strength al-li alloy
US5211910 *Jan 26, 1990May 18, 1993Martin Marietta CorporationUltra high strength aluminum-base alloys
US5259897 *Mar 23, 1989Nov 9, 1993Martin Marietta CorporationUltrahigh strength Al-Cu-Li-Mg alloys
US5462712 *Jul 1, 1994Oct 31, 1995Martin Marietta CorporationHigh yield strength, high artificially aged strength, weldability; aerospace, aircraft
US8118950Dec 4, 2008Feb 21, 2012Alcoa Inc.Aluminum-copper-lithium alloys
Classifications
U.S. Classification420/533, 148/439, 148/417
International ClassificationC22C21/00
Cooperative ClassificationC22C21/00
European ClassificationC22C21/00
Legal Events
DateCodeEventDescription
Oct 14, 1997FPAYFee payment
Year of fee payment: 12
Oct 12, 1993FPAYFee payment
Year of fee payment: 8
Oct 16, 1989FPAYFee payment
Year of fee payment: 4
Dec 30, 1986CCCertificate of correction
Nov 14, 1985ASAssignment
Owner name: SECRETARY OF STATE FOR DEFENCE IN HER MAJESTY S GO
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNORS:EVANS, BRIAN;PEEL, CHRISTOPHER J.;REEL/FRAME:004478/0661
Effective date: 19830114